Racket stringing apparatus

ABSTRACT

Apparatus for stringing rackets having a vertical column, a work head assembly rotatably mounted on the column on which the racket is clamped, a tensioning assembly mounted on the column for releasably grasping and tensioning a string threaded through a pair of apertures in the racket frame, and a string clamping assembly carried by the work head assembly below the racket frame to releasably maintain the string under tension when the tensioning assembly is released. The string clamping assembly includes an electromagnet mounted for sliding vertical movement with respect to the base of the string clamping assembly. When downward pressure is exerted on the electromagnet, a breaker point assembly is actuated to energize the electromagnet and thereby lock the base to the work head assembly. A manually actuated switch is provided for deenergizing the electromagnet and a spring thereupon returns the electromagnet to its upper inactive position.

United States Patent 1 Smith Oct. 21, 1975 RACKET STRINGING APPARATUS[75] Inventor: Melvin William Smith, Alta Lorna,

Calif.

[73] Assignee: The Garcia Corporation, Teaneck,

22 Filed: Apr. 25, 1974 21 App]. No.: 464,246

[52] US. Cl 273/73 A; 73/145; 81/126;

269/95; 335/290 [51] Int. Cl. A63B 51/14 [58] Field of Search 273/73 A;73/145; 269/8,

FOREIGN PATENTS OR APPLICATIONS 209,777 8/1957 Australia 273/73 APrimary Examiner-Anton O. Oechsle Attorney, Agent, or Firm-Fitzpatrick,Cella, Harper & Scinto [5 7 ABSTRACT Apparatus for stringing racketshaving a vertical column, a work head assembly rotatably mounted on thecolumn on which the racket is clamped, a tensioning assembly mounted onthe column for releasably grasping and tensioning a string threadedthrough a pair of apertures in the racket frame, and a string clampingassembly carried by the work head assembly below the racket frame toreleasably maintain the string under tension when the tensioningassembly is released. The string clamping assembly includes anelectromagnet mounted for sliding vertical movement with respect to thebase of the string clamping assembly. When downward pressure is exertedon the electromagnet, a breaker point assembly is actuated to energizethe electromagnet and thereby lock the base to the work head assembly. Amanually actuated switch is provided for deenergizing the electromagnetand a spring thereupon returns the electromagnet to its upper inactiveposition.

3 Claims, 16 Drawing Figures U.S. Patent Oct. 21, 1975 Sheet '1 0143,913,912

US. Patent Oct.21,1975 Sheet40f4 3,913,912

n Ti 3.15.

98 W15 30 h m K RACKET STRINGING APPARATUS This invention relates tomachines used for the stringing of rackets, such as tennis rackets orthe like, for example. Machines of this type usually include acounterweight mechanism adapted to tension a string which has just beenpassed through a pair of corresponding apertures in the racket frame inorder to form one of the strand elements. Generally, the longitudinalstrands are strung first followed by the transverse strands. A clampingdevice is provided which clamps the string after the tensioning thereof,within the racket frame close to the outlet aperture. Once the strandunder tension of the tensioning device is clamped, the tensioning deviceis released and the free end portion of the string is passed through thenext pair of apertures in the frame. The racket is turned 180 so thatthe outlet aperture is adjacent the counterweight mechanism and the newstrand is tensioned thereby. This process is continually repeated foreach strand until the stringing operation is completed.

Related patents in this art include: U.S. Pat. No. 2,309,849 issued Feb.2, 1943; U.S. Pat. No. 3,511,502 issued May 12, 1970; U.S. Pat. No.3,635,080 issued Jan. 18, 1972; U.S. Pat. No. 2,114,216 issued Apr. 12,1938; U.S. Pat. No. 2,188,250 issued Jan. 23, 1940; U.S. Pat. No.2,154,870 issued Apr. 18, 1939; U.S. Pat. No. 2,262,110 issued Nov. 11,1941; U.S. Pat. No. 1,969,826 issued Aug. 14, 1934; U.S. Pat. No.3,441,275 issued Apr. 29, 1969; and U.S. Pat. NO. 2,000,948 issued Nov.30, 1937.

The present invention involves a new combination of elements combined insuch a way as to provide a new and improved racket stringing machinewhich speeds up production, which is less fatiquing to the operator,which provides uniformity of tension, which is a selfcontained unit andwhich requires minimum operator skill.

In one form thereof the present invention contemplates the provision ofa new and improved machine for stringing rackets having a frame providedwith pairs of apertures for the passage of a string which forms strandsbetween the apertures. The apparatus comprises, in combination, avertically disposed column, a work head assembly rotatably mounted onthe column, a tensioning assembly also mounted on the column forreleasably grasping and tensioning a string threaded through a pair ofthe apertures in the racket frame, acting exteriorly of the frame, and astring clamping assembly carried by the work head assembly below theracket frame to releasably maintain the string under tension when thetensioning assembly is released.

According to one aspect of my invention the tensioning assembly ischaracterized by a reciprocating bar, an air cylinder and pistonassembly, a connecting member interconnecting the air cylinder andpiston assembly with the reciprocating bar, compressor means foractuating the air cylinder and piston assembly, an upright post fixedlymounted on one end of said reciprocating bar having an inclined upperend portion, a rod pivotally mounted on the post and having an upperrounded serrated portion, and means for resiliently urging the serratedportion and the inclined upper end portion to releasably grasp thestring therebetween.

According to another aspect of my invention, the string clampingassembly is characterized by a base and electromagnetic means forreleasably locking the base to the work head assembly in a selectedposition on the work head assembly.

There has thus been outlined rather broadly the more important featuresof the invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be disclosed more fullyhereinafter. Those skilled in the art will appreciate that theconception on which this disclosure is based may readily be utilized asthe basis for the designing of other structures for carrying out theseveral purposes of the invention. It is important, therefore, that thisdisclosure be regarded as including such equivalent constructions as donot depart from the spirit and scope of the invention.

One embodiment of the invention has been chosen for purposes ofillustration and description, and is shown in the accompanying drawings,forming a part of the specification, wherein:

FIG. 1 is a perspective view of a racket stringing machine constructedin accordance with the concepts of my invention;

FIG. 2 is a longitudinal sectional view of the racket stringing machineof FIG. 1 showing the initial step of passing a string through a pair ofcorresponding apertures in a racket frame;

FIG. 3 is a view similar to FIG. 2, but showing the tensioning of thestring so passed;

FIG. 4 is a view similar to FIG. 3, but showing the step of clamping theso tensioned string and thence releasing the tensioning device;

FIG. 5 is a view similar to FIG. 4, but showing the racket frame afterit has been rotated with respect to the string tensioning means;

FIG. 6 is a view similar to FIG. 5, but showing the next strand beingtensioned;

FIG. 7 is a plan view drawn on a reduced scale showing the stepillustrated in FIG. 2;

FIG. 8 is a plan view drawn on a reduced scale showing the stepillustrated in FIG. 3;

FIG. 9 is a plan view drawn on a reduced scale showing the stepillustrated in FIG. 4;

FIG. 10 is a plan view drawn on a reduced scale showing another aspectof the step illustrated in FIG.

FIG. 11 is a plan view drawn on a reduced scale showing the stepillustrated in FIG. 5;

FIG. 12 is a plan view drawn on a reduced scale showing the stepillustrated in FIG. 6;

FIG. 13 is an enlarged, longitudinal, medial, sectional view of a baseassembly of a clamping device constructed in accordance with the conceptof this invention;

FIG. 14 is a view similar to the view of FIG. 13, but showing the baseassembly in its clamping position and also showing the portion of thedevice which clamps the strings;

FIG. 15 is a fragmentary view of the portion of the device which clampsthe strings in its clamping position; and

FIG. 16 is a sectional view taken along the line indicated at 1616 ofFIG. 15.

Referring to the drawings in detail, and initially to FIG. 1, there isshown a racket stringing machine comprising a base 10 with a column 12mounted thereon. A tray assembly 14 extends partially around the col- 1umn and a rotatable work head assembly 16 is mounted on a spindle 18 atthe top thereof. Clamp supports 20 carry clamp members 22 which, bymeans of bolt and Wing: nut assemblies 23, cooperate to releasablyhold'a racket frame 24 during the stringing operation. Mounted insidethe column 12 is a compressor assembly, indicated generally at 26, foractuating a tensioning assembly, indicated generally at 28, as will bedescribed more fully hereinafter.

After'the racket frame 24has been secured by the clamps 22, thestringing operation commences. As best seen in FIGS. 2 and 7, a string30 is knotted, as at 32, and threaded through-oppositely disposedapertures 34 and 36 in the racket frame. The work head assembly 16,carrying the clamp members 22 and racket frame 24, is rotated on thespindle 18 until the string 30 in the frame is substantially parallel tothe axis of translation of reciprocating bar 38. The reciprocating bar38 is mounted on rollers 40 inside the column 12 with the ends thereofpassing outwardly through openings 42 and 44. An-air cylinder 46 isfixedly mounted within the column 12, as at 48, and carries a piston rod50, which is connected to the reciprocating bar 38 by a connectingmember 52, provided for the purpose. Controlled air pressure is suppliedto the cylinder 46 from the compressor assembly 26 through aconventional value and pipingarrangement, not shown.

Still referring to FIG. 2, the tensioning assembly 28 further includesan upright post 54 fixedly mounted on the end of thereciprocating rod38, as at 56, and a pivotable rod 58 pivotally mounted on the post bymeans of a spring loaded pin 60 so that the rod 58 resiliently engagesthe post 54 in a clamp-like manner. As best seen in FIG. 1, thepivotable rod 58 is provided with a serrated surface 59, and the post 54has an angularly inclined end portion 55in order to effect a goodgripping action of the string therebetween.

In operation, after the string 30 is threaded through the apertures 34and 36, it is looped around the pivotable rod 58 and clamped between therod 58 and the post54, as shown in FIG. 2. Air is then supplied to theair cylinder 46 in order to move the reciprocating rod 38 from itsposition asishown in FIGS. 2 and 7 to its position as shown in FIGS. 3and 8. The air pressure is selected, as indicated by gauge 62, FIG. 1,so that the proper tension is maintained on the string 30. The next stepin the stringing operation is to move string clamping assembly,indicated generally at 64, to a position adjacent the aperture 36 in theracket frame 14, and the clamp (described more fully hereinafter) ismoved to its clamping position to grip the string, as shown in FIG. 9.Then, the rod 38 is returned to its initial position, and the string isreleased from the tensioning assembly 28, as shown in FIGS. 4 and 10.The work head assembly 16 and the racket frame 24 are then rotated 180from their positions as shown in FIGS. 4 andto their positions as shownin FIGS. 5 and 11, and the string 30 is passed through the next pair ofoppositely disposed apertures 66 and 68, as shown in FIGS. 6 and 12. Thestring is again passed around the pivotable rod 58 andclamped betweenthe rod 58 and the post 54, and the reciprocating rod 38 is movedoutwardly to again tension the string, as seen in FIGS. 6 and 12.Thence, the string clamping assembly 64 is released as shown in FIG. 12.The foregoing steps are then repeated until the stringing operation iscompleted. For

stringing the transverse strands in the racket, the same steps areemployed except that initially the work head assembly 16 is only rotated90. It will be appreciated that by controlling the air flow and pressureto the air cylinder 46 the speed of the tensioning and the stringingpressure may be selected as desired for each racket, and constant stringtension is maintained for all strands in the racket. I

Asbest seen in FIGS. 13 to 16, the string clamping assembly 64 includesa sliding base which, preferably, is fabricated from a material such asnylon, for example. Fixedly mounted on the base is an upwardlyprojecting vertical slide tube 72. Mounted over the base 70 is acup-shaped magnet body housing 74 fabricated from aluminum or the likematerial. An electromagnet 76 is fixedly mounted within the magnet bodyhousing 74, and the inside diameter thereof is adapted for slidingmovement as at 78 with respect to the base 70. Thus, the magnet 76 andthe housing 74 are arranged for limited vertical movement with respectto the base 70. A spring member 80 is interposed between the base 70 andthe housing 74, which urges the housing 74 upwardly with respect to thebase 70, and a O- ring 82, mounted on the vertical slide tube 72, servesto limit the upward travel of the housing 74 and the electromagnet 76and thereby locks the assembly together. As best seen in FIG. 13, amagnet breaker point assembly 84 has one lead 86 connected to theelectromagnet 76 and a second lead 88 connected to an electrical pinjack 90, which receives power from a suitable power source, not shown,such as a 12 volt DC power source, for example, through a switch 92 thatreverses the polarity of the power source when actuated. A set screwserves to adjust the setting of contacts 87 and 89 of the breaker pointassembly 84.

'In operation, the string clamping assembly 64 is moved into its desiredposition on the work head assembly 16, FIG. 1, by sliding the base 70 onthe upper surface of the work head assembly. When the assembly is in itsdesired location, downward pressure is exerted on the magnetic bodyhousing 74 to move the housing 74 and the electromagnet 76 from theirupper positions as seen in FIG. 13 to their lower positions as seen inFIG. 14. This motion closes the contacts in the breaker point assembly84 and activates the electromagnet 76 so that the magnet firmly locksthe string clamping assembly in position on the work head assembly 16.When it is desired to release the clamping assembly 64, the switch 92,which may be located in any convenient accessible location such as onthe column 12, for example, is actuated to reverse the polarity from theDC power source, thereby momentarily repelling the magnet 76 and openingthe contacts in the breaker point assembly 84. The spring 80 will nowhold the breaker point assembly 84 open and return the body 74 and themagnet 76 to their upper inactive positions, as seen in FIG. 13. Theclamping assembly is then ready to slide freely on the work headassembly 16 to its next position.

The string clamping assembly 64 further comprises a clamp body 94, whichis mounted in the vertical slide tube 72, FIG. 14. As seen in FIGS. 14and 16, the upper end of the body 94 is in the form of an upwardlyopening fork. A flat member 96 is secured to the inner side of one ofthe branches of this fork, and a plurality of hooked or bent fingers 98extend from the upper edge thereof to form the fixed jaw of a clampingdevice. A

mating movable jaw of vertical teeth 100 is adapted to engage thefingers 98, respectively. The teeth 100 are formed along the upper edgeof a plate 102 adapted to slide against the flat member 96. The plate102 has a lower, integral rod-like guiding tail 104, which is axiallyslidable in the body 94, and a transverse pin 106 is also carried bythis plate. An actuating lever 108 is hinged on the pin 106 and has oneend pivotally attached to one end of a link 110, as at 112. The otherend of the link 110 is hinged on a pin 114, which is eccentricallycarried by a gudgeon 116 that is lockable in a selected angular positionin the body 94, such as by a set-screw not shown.

In operation, when it is desired to clamp the string 20 in the stringclamping assembly 65, the string is placed between the fingers 98 andthe teeth 100 and the actuating lever is swung downwardly from itsposition as seen in FIG. 14 to its position as seen in FIG. 15. Thus,the lever 108 is swung about the pin 106 and the plate 102 is displacedvertically on the member 96, the latter being formed with a verticalguiding groove for this purpose in which the pin 106 slides, to therebybring the teeth 100 up into the bent portion of the fingers 98 to clampthe string. When the axis of the pins 106, 112, and 114 aresubstantially in alignment, as seen in FIG. 15, the fingers 98 and theteeth 100 remain in their clamped positions, the force of the clampingaction being adjustable by the angular position of the gudgeon 116. Inorder to release the string, the actuating lever 108 is returned fromits position as seen in FIG. 15 to its position as seen in FIG. 14, tomove the teeth 100 away from the fingers 98 and thereby release thestring.

It will thus be seen that the present invention does indeed provide animproved racket stringing apparatus which is superior in operability,reliability and efficiency as compared to prior art such devices.

Although a particular embodiment of the invention is herein disclosedfor purposes of explanation, various modifications thereof, after studyof this specification will be apparent to those skilled in the art towhich the invention pertains.

What is claimed and desired to be secured by letters patent is:

1. In a racket stringing apparatus for stringing rackets having a frameprovided with pairs of apertures for the passage of a string which formsstrands between the apertures, said apparatus having a substantiallyvertically disposed column, a work head assembly rotatably mounted onsaid column about a substantially vertical axis and on which the frameof the racket to be strung is clamped, the combination comprising astring clamping assembly positionable on said work head assembly belowsaid racket frame to releasably act on said string threaded through saidpair of apertures adjacent said frame to releasably maintain said stringunder tension,

said string clamping assembly comprising a base, electromagnetic meansfor releasably locking said base to said work head assembly in aselected position on said work head assembly,

said electromagnetic means of said string clamping assembly comprisingan electromagnet surmounted on said base for sliding vertical movementwith respect to said base, means for actuating said magnet when downwardpressure is exerted on said magnet to lock said base to said work headassembly, and means for releasing the magnetic force and returning themagnet to its upper inactive position.

2. A string clamping assembly according to claim 1 wherein said meansfor actuating said magnet comprise a magnet breaker point assemblyclosable when said downward pressure is exerted, and wherein said meansfor releasing the magnetic force and returning the magnet to its upperinactive position includes means for reversing the polarity of saidmagnet and spring means for holding open the breaker point assembly andurging the magnet to its upper inactive position.

3. Racket stringing apparatus for stringing rackets having a frameprovidedwith pairs of apertures for the passage of a string which formsstrands between the apertures, said apparatus in combination comprisinga substantially vertically disposed column, a work head assemblyrotatably mounted on said column about a substantially vertical axis andon which the frame of the racket to be strung is clamped, a tensioningassembly mounted on said column for releasably grasping and tensioning astring threaded through a pair of said apertures in the racket frame,said tensioning assembly acting on the portion of said string exteriorto said racket frame, said tensioning assembly comprising areciprocating bar, an air cylinder and piston assembly, a connectingmember interconnecting said air cylinder and piston assembly with saidreciprocating bar, means for actuating said air cylinder and pistonassembly, means mounted on one end of said reciprocating bar forreleasably grasping and tensioning said string; a string clampingassembly carried by said work head assembly below said racket frame toreleasably act on said string threaded through said pair of aperturesadjacent said frame to maintain said string under tension when saidtensioning assembly is released, said string clamping assemblycomprising a sliding base, means mounted on said base for releasablygrasping said string, a magnet body housing surmounted over said base,an electromagnet fixedly mounted within said housing having an insidesurface adopted for sliding movement with respect to said base, a springmember interposed between said base and said housing for urging saidhousing upwardly with respect to the base, means for limiting the upwardtravel of said housing, an electrical pin jack, a magnet breaker pointassembly having one lead connected to said electromagnet and having asecond lead connected to said jack, a polarity reversing switch meansfor receiving power from a DC power source, said jack being connected tosaid switch means, whereby said string clamping assembly is movable intoits desired position on the work head assembly by sliding the base onthe upper surface of the work head assembly and when in its desiredposition downward pressure exerted on said magnetic body housing movessaid electromagnet into engagement with said surface of said work headassembly and closes the contacts in the breaker point assembly toactivate the magnet so that the magnet holds the string clampingassembly in said position on the work head assembly and wherebyactuation of said switching means reverses the polarity from the DCpower source to momentarily repel the magnet and open the contacts inthe breaker point assembly so that the spring member holds the breakerpoint assembly open and returns the magnet and the housing to theirupper inactive positions.

1. In a racket stringing apparatus for stringing rackets having a frameprovided with pairs of apertures for the passage of a string which formsstrands between the apertures, said apparatus having a substantiallyvertically disposed column, a work head assembly rotatably mounted onsaid column about a substantially vertical axis and on which the frameof the racket to be strung is clamped, the combination comprising astring clamping assembly positionable on said work head assembly belowsaid racket frame to releasably act on said string threaded through saidpair of apertures adjacent said frame to releasably maintain said stringunder tension, said string clamping assembly comprising a base,electromagnetic means for releasably locking said base to said work headassembly in a selected position on said work head assembly, saidelectromagnetic means of said string clamping assembly comprising anelectromagnet surmounted on said base for sliding vertical movement withrespect to said base, means for actuating said magnet when downwardpressure is exerted on said magnet to lock said base to said work headassembly, and means for releasing the magnetic force and returning themagnet to its upper inactive position.
 2. A string clamping assemblyaccording to claim 1 wherein said means for actuating said magnetcomprise a magnet breaker point assembly closable when said downwardpressure is exerted, and wherein said means for releasing the magneticforce and returning the magnet to its upper inactive position includesmeans for reversing the polarity of said magnet and spring means forholding open the breaker point assembly and urging the magnet to itsupper inactive position.
 3. Racket stringing apparatus for stringingrackets having a frame provided with pairs of apertures for the passageof a string which forms strands between the apertures, said apparatus incombination comprising a substantially vertically disposed column, awork head assembly rotatably mounted on said column about asubstantially vertical axis and on which the frame of the racket to bestrung is clamped, a tensioning assembly mounted on said column forreleasably grasping and tensioning a string threaded through a pair ofsaid apertures in the racket frame, said tensioning assembly acting onthe portion of said string exterior to said racket frame, saidtensioning assembly comprising a reCiprocating bar, an air cylinder andpiston assembly, a connecting member interconnecting said air cylinderand piston assembly with said reciprocating bar, means for actuatingsaid air cylinder and piston assembly, means mounted on one end of saidreciprocating bar for releasably grasping and tensioning said string; astring clamping assembly carried by said work head assembly below saidracket frame to releasably act on said string threaded through said pairof apertures adjacent said frame to maintain said string under tensionwhen said tensioning assembly is released, said string clamping assemblycomprising a sliding base, means mounted on said base for releasablygrasping said string, a magnet body housing surmounted over said base,an electromagnet fixedly mounted within said housing having an insidesurface adopted for sliding movement with respect to said base, a springmember interposed between said base and said housing for urging saidhousing upwardly with respect to the base, means for limiting the upwardtravel of said housing, an electrical pin jack, a magnet breaker pointassembly having one lead connected to said electromagnet and having asecond lead connected to said jack, a polarity reversing switch meansfor receiving power from a DC power source, said jack being connected tosaid switch means, whereby said string clamping assembly is movable intoits desired position on the work head assembly by sliding the base onthe upper surface of the work head assembly and when in its desiredposition downward pressure exerted on said magnetic body housing movessaid electromagnet into engagement with said surface of said work headassembly and closes the contacts in the breaker point assembly toactivate the magnet so that the magnet holds the string clampingassembly in said position on the work head assembly and wherebyactuation of said switching means reverses the polarity from the DCpower source to momentarily repel the magnet and open the contacts inthe breaker point assembly so that the spring member holds the breakerpoint assembly open and returns the magnet and the housing to theirupper inactive positions.